Heating unit control circuit



March 30, 1954 v. WOODLING 5 5 HEATING UNIT CONTROL CIRCUIT Filed Oct.21, 1948 4 Sheets-Sheet 2 5 7- A LTER/VA 7'//v CURRENT SOURCE 8 IUL 74I? BM QkINVENTOR. jwmw-M w 5 4:;

March 1954 i G. v. WOODLING 7 HEATING UNIT CONTROL CIRCUIT Filed Oct.21, 1948 4 Sheets-Sheet 3 AL TEJQNA T/NG A L TERNA 77M CURRENT l sou/aceI ALTER/VA TING CURRENT SOURC March 30, 1954 v. WOODLING HEATING UNITcormzox. CIRCUIT 4 Sheets-Sheet 4 Filed Oct. 21, 1948 ALTER/VATl/VGCUIZQE/VT SOUKCE AL T'R/VA TING CURRENT sou/ace OUTPUT Patented Mar. 301954 UNITED STATES PATENT OFFICE Claims; 1'

The invention relates in general to electrical heating appliances andmore particularly to household heating appliances which may becontrolled by a controllable space discharge device and which utilizes ametallic film impedancev for the heating: element;

An object of the invention is to provide a household electricfiatironwith rectified alternating current energy from a rectifiercontrolled by a temperature responsive impedance in heat exchangerelationshipwith the fiatiron.

Another object ofthe invention is to provide a temperature responsiveimpedance in heat exchange relationship with a household electricalheating. appliance to affect a bridge circuit and thus control acontroll'ablerectifier supplying energy to the appliance, and further toplace such impedance in circuit relation with the energy output of therectifier.

Another object of the invention is to provide a household electricheating appliance wherein the heating element is a metallic resistorfilm deposited on a dielectric coating which is in turn supported by ametal carrier.

A still further object of the invention is to provide a householdelectric appliance adaptedto be heated by a metallic film heatingelement with such film deposited on a dielectric coating and wherein themetallic film is supplied with electrical energy from a controllablerectifier, and a control circuit has a temperature responsive impedancein heat exchange-relationship with the heating element to control thecontrollable rectifier.

A still further object of the invention is to provide a householdelectric appliance adapted to be heated by' aheating element suppliedwith electrical energy from a controllable rectifier, and a controlcircuit has a temperature responsive element in heat exchangerelationship with the heating element to control the controllablerectifier, and wherein either or'both of the elements may bea metallicfilm.

Figure 1 is a plan view of a metallic carrier supporting a dielectriccoating which in turn supports a metallic filmimpedance used as aheating element;

Figure 2 is a cross-sectional view of Figure 1.- showing the metallicfilm in exaggerated thickness;

Figure '3 is a sectional elevational' view of a fiatiron incorporating ametallic film heating element;

Figure 4 ice sectional plan view taken on the line- 4"-4'- of" Figure 3}Figure 5' is a partial sectional elevational view of a modified form offiatiron incorporating a metallic film impedance;

Figure 6 is a circuit diagram of a controllable supply circuit for theheating element;

Figure 7 is a vector diagram of the voltages obtainable from the circuitof Figure 6;

Figure 8 is another controllable supply cir cuit for the heatingelement;

Figure 9 is a further modification of a controllable supply circuit;

Figures 10 and 11 are still further modifications of a controllablesupply circuit;

Figure 12 is a circuit diagram of a controllable energization circuitwhich incorporates a portion of the heating element in the phase shiftbridge control circuit;

Figure 13 is a vector diagram of the vectors obtainable from the circuitof Figure 12;

Figure 14 is a modification of the circuit of Figure 12';

Figure I5 is a vector diagram of the vectors obtainable from the circuitof Figure 14;

Figure 1 6 is a controllable energization cir cult for a heatingappliance having a control impedance in the heating appliance; and

Figure 17: is a vector diagram of the vectors obtainable from thecircuit of Figure 16;

Figures 1 and 2' illustrate one form oftheinvention wherein a metalliccarrier 2| has recessed portions 22' and and the entire upper surface 23is covered with a dielectric or vitreous enamel coating M. Terminalplates 25 are adapted to be attached or imbedded in the dielectriccoating 2'4 at the recessed portions 22 and remain fixedly in place. Ametallic film impedance Z6 is adapted to be deposited in any well-knownmanner upon the dielectric coating 24 and terminal plates 25. A seconddielectric coating 21 is adapted" to cover the metallic film impedance2B and to extend down over the sides to the metallic" carrier 21 to actas electrical insulation and for instance, the heating unit might beused as a hot plate or other appliance wherein a smooth working surfacewould be desirable. Electrical connectionto the metallic film impedanceis made bythe terminal plates 25 since these terminal plates aredirectly in contact with the metallic film impedance 26. Terminal wiresIl may be attached to the terminal plates by any well-known means suchas soldering or brazing, and in the Figures 1 and 2 have been shown asbeing attached to the underside of the terminal plates and gainingaccess to such terminal plates through holes IS in the metallic carrier2|.

The Figure 2 shows the layers of dielectric coating and metallic film incross section and it is to be understood that this cross-sectional viewis considerably exaggerated, especially as to the thickness of themetallic film impedance.

The Figures 3 and 4 show a metallic film impedance as applied to ahousehold heating appliance shown as an electric fiatiron 29. Thefiatiron 29 includes a metal soleplate 3!] having a working surface 3|and an opposite surface 32. A dielectric coating such as a vitreousenamel coating 33 is adapted to cover the opposite surface 32 of themetal soleplate 33 to act as an insulator. Such dielectric or vitreousenamel coating 33 may be applied in liquid state and may be such coatingthat is fired to a hard, glossy surface covering the opposite surface32. A metallic film impedance 34 may be deposited on the dielectriccoating 33 as the heating element of the fiatiron 29. A seconddielectric coating 35 covers the metallic film impedance 34 to providephysical protection to the metallic film impedance 34 and to act as anelectrical and heat insulator. The heating element may be made insubstantially the same manner as is used in the trade in making thinmetallic film resistors. The vitreous enamel physically protects thethin metal resistor film from abrasion and moisture. With this type ofconstruction, the entire electrical appliance may be washed withoutdamage to the heating element and. thus is rendered sanitary. Theresistor film may have zero, negative or positive temperaturecoefficient. Metal terminal plates 36 and 31 have been shown at the toeand heel portions of the fiatiron 29 to provide electrical connection tothe metallic film impedance 34. These metal terminal plates 36 and 31have been shown as being placed on the first dielectric coating 33whereupon the metallic film impedance 34 is deposited on these metalterminal plates as well as on the first dielectric coating 33. The metalterminal plates 36 and 31 provide suificient thickness of metal toprovide electrical connection to the wires 38 and 39 such as bysoldering or brazing at the terminals 40. The wires 38 and 39 may bejoined into a cable 4I having a conventional male electrical plug 42.

A solid heat insulating cover 43 may cover the entire opposite surface32 of the soleplate 30. This cover 43 may be of any solid insulator suchas a plastic or any other well-known insulating substance. The cover 43has a handle portion 44. The cover 43 is adapted to be fastened to thesoleplate 30 by cap screws which thread edly engage projecting lugs 46on the opposite surface 32 of the soleplate 30 and preferably the capscrews 45 are recessed in the cover 43 as at 41.

The fiatiron shown in Figures 3 and 4 is an improved form of fiatironsince the use of the metallic film impedance 34 permits lightweightconstruction of the fiatiron, and also permits a minimum thicknessbetween the working surface 3| andthe upper surface 48 of the cover 43.

'The Figure 5 shows a portion of a fiatiron iii) I43 that differs insome particulars from the fiatiron 29 of Figures 3 and 4. A plate I4Imay e made of metal as is the usual custom and has a recess I42 toreceive a terminal plate I43. Between the terminal plate I43 and therecess I42 is a dielectric coating I44 which completely covers the lowersurface of the plate IN. A metallic film impedance I45 is deposited onthe dielectric coating I44 and is, hence, in electrical contact with theterminal plate i43. A second dielectric coating I43 is deposited on themetallic film impedance I45 and also preferably covers the toe portionI41 of the plate I4I as well as the entire edges of the plate I4I, forelectrical insulation and for mechanical protection to the metallic filmimpedance I45. By providing a fiat surface to the first dielectriccoating I44 the metallic film impedance I45 and the second dielectriccoating I43 will also have a fiat surface to thus provide asmoothworking surface for the fiatiron I40. Such fiat surface may beobtained by grinding or other suitable method to eliminate anyunevenness. A hole I48 is provided in the plate I4I so that a terminalwire I49 may gain access to the terminal plate I43 and be electricallyconnected thereto in any suitable. man- The circuit of Figure 6 shows anenergization circuit 53 which may be controlled in electrical. outputfor energizing the heating element of a household electrical appliance.A household heating appliance 5I has been shown in dotted lines toindicate a fiatiron having a heating element 52. The energizationcircuit 53 is preferably housed in a separate housing as indicated bythe dashed line 54. The energization circuit 53 includes generally atransformer 55 having a primary 56 energizable from an alternatingcurrent source 51 through the switch 58. A secondary 59 of thetransformer 55 energizes the anodes 63 of space discharge devices 6].These space discharge devices have been shown as gaseous discharge tubeshaving a control element such as control grids 62. The space dischargedevices have been shown as constituting a full wave rectifier systemhaving a rectified alternating current output deliverable across theoutput terminals 63 and 64. The rectified output of the rectifiers fiIis delivered to the heating element 52 for energization thereof.

The energization circuit 53 also includes a control circuit 65 having aphase shift bridge 66 energized from a transformer winding 61. The phaseshift bridge 65 has four arms with the first arm I5 including a manuallyvariable resistance B8 and a capacitive element 69. The second armincludes an impedance I3 shown as a resistance. The third arm is atemperature responsive impedance II that is shown in heat exchangerelationship with the heating element 52. In this case, the temperatureresponsive impedance II is shown as being enclosed within the confinesof the fiatiron 5i. The fourth arm of the bridge 65 includes anotherimpedance shown as a resistance T2. The output of the bridge 63 atterminals I4 and It is supplied to a grid transformer I3 to variablyshift the phase of the grid-cathode voltage relative to theanode-cathode voltage of the space discharge devices 6|.

The vector diagram of Figure 7 may be referred to as an aid inunderstanding the operation of the circuit of Figure 6. In all thefollowing vector diagrams the voltage vectors will be given a referencecharacter corresponding to'the reference character of the voltage sourceor im pedance "across which vthe voltage drop occurs; Similarly, a pointpotentia'l will'be given a reference character corresponding to the:reference character of thexterminal, juncture or pointin the circuit.The vector .6?! designates the alternating :current input voltage to thebridge 66 which will be in phase with :the alternating currentvoltage-applied to the anodes 60. The vectors 11 and 1,2 lie alongthe'vector 61. The juncture 14 between the impedances =1! and I2 isshown as the point 74 on the vector diagram of Figure 7. The juncture 76between the capacitance element GS-andimpedance "It is-shown on thevector diagram by the reference character 16. The first arm of @thebridge it which includes :the variable resistance 68 and the capacitanceelement 69 is shown on the vectordiagram of Figure 7 by the vector 75.Similarly, the impedance 10 has a vector-1B on the vector diagram. Theoutput voltage of the phase shift bridge-66 that is applied to the gridtransformer T3 is shown by the vector output The direction of the vectorshown on this vector diagram indicates that the output voltage lags theinput voltage 61 by an angle approximately 90 degrees. This would permitthe rectifiers 6| .to trigger or fire-at a time phase 90 degrees laggingthe anode-cathode voltage. The variable resistance 68 may be manuallyadjusted to shift the location of the point .16 to thus adjust thefiring angle, of the space discharge device "6i and hence adjust therectified output to the heating element 52. The temperature responsiveimpedance 1| which is in heat'exchange relationship with the heatingelement 52 should have a posi tive temperature coeflicient such that asthe heating element 52 tends to overheat, the impedance of thetemperature responsive impedance H will increase to decrease the firingangle of the rectifier 6i and hence decrease the electrical output tothe heating element 52. Thus, the phase shift bridge 66 of the controlcircuit maintains-a substantially constant temperature of the heatingelement 52.

Figure 8 shows a modification of the energizetion circuit of :Figure 6.In this case, the rectifier circuit has beenshown as a half waverectifier circuit 19 that supplies energy to the heating element 52 of aheating appliance 5i which has again been shown as a flatiron. Atransformer winding 61 again supplies energy to a phase shift bridge at.This phase shift bridge isishown as having first and second temperatureresponsive 'impedances 8| and '82 positioned in heat exchangerelationship with the heating element 52. The juncture 83 between theimpedances Bil and 82 is connected to pneline at of the rectifiercircuit 7:9. The connection be tween this juncture 83 and the line 84has been shown as being made within the flatiron 5! in order that onlyfour wires need be connected to the fiatiron 5|. The phase shift bridge8Q has first and second arms -85 and ,86 with a juncture 81therebetween. The output of the bridge 80 is between the junctures ,83and .8! and a1) plied to the cathode and grid of the rectifier of therectifier circuit 19. The first temperature responsive impedance 8|preferably has :a -pcsitive temperature coefiicient and the secondtemperature responsive impedance 82, 'a negative temperaturecoefiicient. By so providing positive and negative temperature'coefilcienlts the bridge :80 will be approximately twice as sensitiveasthebridge 66 of the circuit of Figure 6. It will "be obvious that thefirst temperature re- 6 sponsive impedance may have any givenr temperature icoeflicient'and theicircuit will :operate properly. if the secondtemperature responsive impedance82 has a temperaturecoefiicient' that ismore negative orplesspositive than said given :temperature ccefiicient.

The vector diagram for the circuit of Figure-8 willw;be;essentially*thezsame as the vector diagram of Figure-7 except thatthere will be two temperature responsive 'impedances that vary withtemperaturelchanges rather thanronly one.

The circuit of Figure '9 shows a :still further modification of acontrollable energization circuit .90 having a half Wave rectifiercircuit 9|. In this case, the heating element 52 is again supplied withenergy from the rectifier circuit 91,:but'the heating 'elementtz is notin the household appliance which vhas been shown as'a cordless fiatiron9'2. Theiheating element is mounted'withinacontainer .93. The container93 may be considered as a hot plate for heating the appliance or*flatiron 92 and maintaining same at a substantially constanttemperature as long as this flatiron 92 is in contact with the hot platesurface 94 01 the container 93. The arrangement shown in the circuit ofFigure 9 may well be used for cordless automatic fiatirons or as aheating surface for any type of appliance such as'a hot plate, oven :orgrill of a stove. The controllable energization circuit includes a phaseshift bridge 95 having four arms .96., '91, 98 and 99, all of which havebeen :shown as being in heat exchange relationship with the heatingelement 52 within the container "93. In order to make this phase shiftbridge 95 as sensitive as vpossible, the impedances of the first andfourth arms 96 and 99 should have a positive temperature coefiicient,and the impedances of the second and third arms 91 and .98 should have anegative temperature coefiicient. The vector diagram for the circuit ofFigure 9 will be essentially the same as the vector diagram shown inFigure '2 except that all four impedances of the bridge are temperatureresponsive in order to make the 5 bridge 95 approximately four times assensitive as the bridge 66 of the circuit of Figure 6. The arm 98 .isshown as having a variable condenser mo therein to permit manualadjustment of the operating temperature of the heating element52.Obviously, a variable resistor may be utilized for this purpose as incircuits described above; however, the variable condenser may haveadvantages of not being affected by the heat produced in the container93 since it will have no movable contact surfaces as is the usual casewith variable resistors. Further, the variable condenser may have atemperature coefficient other than zero and arnegative temperaturecoeiiicient would still further increase the-sensitivity of the bridge95.

The circuit of Figure '10 also shows a controllable energization circuit32 having a metifier I03 :forsupplying rectified alternating currentenergy to the heating element 52. A household appliance IM has beenshown as a cooking vessel-adapted to be placed in heat exchangerelationshipwith the heating element 52 as by placing this cookingvessel Ills on a heating surface [950i a container which contains theheating element 52. The cooking vessel H34 has been shown as 'havingacontrol impedance la! incorporated into this cooking vessel I04 whichcontrol impedance m1 is onearm of a phase shift bridge I08. The bridge108 controls the firing angle of the rectifier M3. The control impedance(-0! has a temperature coefiicient other than zero in order to controlthe output of the phase shift'bridge I08 and, hence, control the outputof the rectifier I03. In the circuit as shown, the control impedance I01should have a negative temperature coeflicient. The control impedancemay take many forms and preferably is a metallic film impedance such asshown in the Figures 1-5. Metallic film impedances have been developedwhich may have the temperature coefiicient thereof controlled to a veryhigh degree and thus a metallic film impedance having a very largepositive or negative temperature coeflicient may be selected for use asthe control impedance I01. Such a metallic film impedance may beincorporated into the household appliance I04 in a manner similar tothat shown in Figures 1 and 2 or the method shown in Figures 3, 4 and 5.Electrical connections to such metallic film impedance may be easilyeiiected and these connections and the metallic film impedancethemselves could be made water-tight and to present a smooth surface sothat the household appliance I04 may easily be washed and kept in asanitary condition.

The circuit of Figure 11 shows a still further energization circuit IIiwherein a controllable rectifier I I2 supplies rectified alternatingcurrent energy to a heating element 52. The rectifier H2 is controlledby a control circuit H3 which includes a fixed phase shift supplied bythe resistance H4 and the capacitance H5. The resistance I I4 has beenshown as being variable to vary the output of the rectifier 5 52. Athermocouple II'B has been shown as being in heat exchange relationshipwith the heating element 52, and the output of this thermocouple H issupplied to an amplifier II? which amplifies the voltage obtained fromthe thermocouple I I0 and applies it to the rectifier H2. Thecontrollable rectifier I I2 is controlled by a system known as a D. C.bias-A. C. rider system wherein the resistance and capacitance I I4 andI I supply a fixed phase shift of approximately 90 degrees lagging theanode voltage and the amplified voltage from the thermocouple suppliesavariable direct cur- 1 rent for varying the firing angle of therectifier II2. The thermocouple IIG has been shown as being mountedwithin the heating appliance in close proximity to the heating element52 so that it is in heat exchange relationship with this heating element52. It will be obvious that this thermocouple I I6 may be mounted in aseparate unit such as the arrangement shown in Figure 10.

The circuit of Figure 12 shows a still further controllable energizationcircuit II9 for supply' ing rectified alternating current energy to aheating element I29. The heating element I23 has an intermediateterminal I2 I, and the righthand portion I22 of the heating element I23serves the dual function of a portion of the heating element and also asone arm of a phase shift bridge I23. The controllable energizationcircuit H9 includes a rectifier device I24 for supplying the rectifiedcurrent to the heating element I20 and this rectified alternatingcurrent is preferably filtered by a filter I25 so as to applyessentially pure direct current to the heating element I20. The phaseshift bridge I23 has condensers I26 and I2! in two arms I28 and I33 ofthis bridge M3 to prevent the direct current from flowing in this bridgeI2. The alternating current impedance of the right-hand portion I22 willthen be that used as one arm of the bridge The vector diagram of Figure13 shows the vectors obtainable from the circuit of Figure 12; The firstarm I28 of the bridge I23 is shown by the vector I 28, and likewise thesecond and third arms I29 and I30 are shown by the vectors I29 and I30.The input voltage to the phase shift bridge I23 is shown by the vectorinput and the output voltage of the bridge I23 is shown by the vectoroutput. The right-hand portion I22 of the heating element I20 should beresponsive to temperature changes and, in the circuit as shown, shouldhave a positive temperature coefiicient to make a stable circuit. Thesecond arm I29 has been shown as being variable in order to adjust theoutput of the rectifier I24 and hence the temperature of the heatingelement I20.

The heating element I20 may be constructed of a metallic film impedancewith an intermediate terminal connected thereto in order to supply anelectrical connection as at the intermediate terminal I2I.

Thecircuit of Figure 14 shows an improvement over the circuit of Figure12 wherein only two leads are required to the heating element I3l. Theheating element I3I is again supplied with rectified alternating currentenergy from a rectifier I32 as filtered by a filter I33. The heatingelement I3I has been shown as being inductive which will not impede theflow of the direct current from the rectifier I32; however, it willimpede the flow of alternating current applied to it from a phase shiftbridge I34. This phase shift bridge I34 includes first, second and thirdarms I35, I30 and I31, and the heating element I3! constitutes thefourth arm of this bridge I34.

The vector diagram of Figure 15 shows the vectors obtainable from thebridge I34 wherein the arm I3I may have a high alternating currentimpedance relative to the first and second arms I35 and I36, and hencethis bridge I34 may be made quite sensitive. An advantage of the circuitof Figure 14 is that the heating element I3 I performs the dual functionof heating and control of the rectifier I32. No intermediate terminalsare needed and hence merely the two end terminals of the heating elementI3I need exist. The heating element I3I would thus be desirable for aportable heating appliance such as a flatiron which may then have merelythe two normal wires for electrical connection to such heating elementand need not have any extra wires or any separate control impedance.

Figure 16 is a further modification of the invention wherein aheatingelement I52 is supplied with rectified alternating current energyfrom the rectifier I53. The heating element I52 is adapted to be mountedin a base unit I54 which may have ears I55 as an aid in centering thefiatiron I56 on the base unit I54. The fiatiron I56 has a controlimpedance I51 contained therein and adapted to be in heat exchangerelationship with the heating element i5! when the fiatiron I56 isplaced on a heating surface I58 on the base unit I54. The rectifier I53has a bridge circuit I59 for control of the rectifier I53 and thecontrol impedance I51 is adapted to be placed in parallel with one armI69 of the bridge circuit I59. The electrical connection between thecontrol impedance I51 and the bridge circuit I59 is provided by terminalplates I6I in the fiatiron I56 and terminal plates I52 in the base unitI54. The terminal plates ISI are electrically insulated from thefiatiron I56 by insulators I53 and the terminal plates I62 are insulatedfrom the base unit I54 by insulators I64. The terminal platesv IEI andIE2 may make electrical connection by;

9 surface contact or-preferably by a plug and j'ack connection I65and: IBIL When thefiatiron: is placed upon thehea'ting surface: I581" so thattheterminal plates IBI and I82: are in electricalv contact, then the'control impedance. I512 is in. paralleli with the arm Iiit to reduce-thetotal impedance in this arm of the bridge circuit I59. This is arrangedto cause the phase of the: grid-cathode voltage to lag to agreaterdegree the phase of the anode-cathode voltage ofrthe rectifier I53. Thiswill reduce the electrical: output of the rectifier I53 and reduce the:heat produced by the heating element I52. A fourth arm I69 of the'bridgeI59 is made adjustable toiprovide for the manual variation of theoperation temperature ofv the flat'iro-ni I56.

This-will be the case when the fiatiron 156 is in heat: exchangerelationship with the heating element I52 and the: control impedance I5?isv part of the bridge circuit I59. When the flatironIEIi. is removedfrom the baseunit I54; the control impedance I5I'wi1l no longer beinparal leliwith'the arm IBI! and, hence, the-impedance of such armwillincrease to increase the electrical output of the rectifier: I53.The heating element I52 will then raise in temperature in accordancewith the increased electrical input thereto. When the fiatiron I56 isagain placed on the base unit I52, the. cont-rel impedance I51 will beinshunt with the. arm H39 to reduce the output of: the'rectifier' I53 to avalue which will produce the desired; temperature setting as dictated bythe variable arm I59. However, the stored heat in the base unit I52 willrapidly raise the temperature of the flatircn I55 tothisoperating'temperature. The :controlimpedance I5? should preferablybe of a negative temperature coefficientso that it will havea regulatingef. fect upon-the operation of the bridgecircuit I59 andrectifier I53;Second and third arms I67 and I68 of the bridge I59 may have apositivetemperature coefiicientto control the bridge I59 when the flatironI56-is' removedfrom the base unit I 54 and hence control thetemperature'of the base-unit I52, and in such case the armsl't'i and I68 should be in heat exchange relationship with the' base. unit I52.

The Figure: 17 shows thevector diagram-for the circuit of Figurelfi'wherein IE is the voltage vector for the-arm I69 and output is theoutput voltage of the bridge circuit I59. control-impedance I? is notiii-shunt with the arm I60,- the impedance ofthe armlIifl willin Whenthecrease'tothat shown by thedotted: line vector 7 I60" and theoutputvoltage will shift to a'posi tionless lagging with respect: to theinput, voltage Any of the temperature responsive elements II, 81; 82,96, 81 98,,99;,II6 I22, I3I, I51, I61, and IE8, just as the' sensing"element I01, may be in the form of a metallic impedance film, andconstructed' similarly to that shown in Figures 1 to 5, either as anindividual film or in combination with a separate film as the heatingelement.

Although the invention has'been described'in its preferred'form'with acertain" degree of particularit'y, itis understood" that the presentdisclosure ofthe preferred form has been made only by way of exampleand" that numerous resorted to without departing, from the spirit andthe scope of the invention as hereinafter claimed,

What is claimed is: V

1 An' electronic tubec'ontroP for a household electric heatingappliance;comprising a hous ing' separatefrom said appliance, a gaseousgridcontrolled re'ctifier mounted in said housing and having an inputand an output; means for con meeting said input toan alternating currentsource, means for connecting the output or said rectifier to a heatingelement of said appliance,- a phase shift bridge circuit having inputandoutput means, means for energizing the input means of said' bridgecircuit from said; alternating current source, means for connectingthe'output means or said bridge circuit to said con trolled rectifier tccontrol the output thereof ,said bridge circuit having fourarms, oneofsaid arms having an impedance element responsive to=temperat'urechanges, andmeans for placing'sa'id one arm inelectricalcircuit relation with the separate from said appliance, a'gaseousgrid'con' trolled rectifier mounted in said housing" and having an inputand an output, means for con necting said input to an alternatingcurrent source; means for connecting the output of said' rectifier to'aheating element of said appliance, said heating element being ametallic'film 1m: pedance, a phase shift bridge circuit having in-' putandoutput means, means for energizing the input means of said bridgecircuit fromsaid' al ternating current source, means for connecting theoutput means of said' bridge circuit" to said controlled rectifier tocontrol theo'utput there= of; said bridge circuit having four arms, twoof said arms having a. metallic film impedance" responsiveto'temperature changes with each hav ing a different temperaturecoefficient of impedance, and'means for placing said two arms in heatexchangerelationship with said heating element.

3'. An electronic tube control for a household electric flatiron,comprising a housing separate from said flatiron, a gaseous gridcontrolledlrectifier mounted in said housing and' havii'ig.v an inputand an output, means for connecting said" input to an alternating.current source, means for connecting the output of said rectifier'to aheating element of said fiatiron, said heating element being a metallicfilm impedance, a phase" shift bridge circuit" having input and" outputmeans, means for energizing theinput means of said bridge circuit fromsaid alternating current source, means for connecting the outputmeans ofsaid'bridge circuit to said controlledrectifierto control the outputthereof; said-bridge circuit having four arms, two of said arms having,an impedance responsive to temperature changes with each having adifierenttemperature coefiicient of: impedance, and means for placingsaid two armsin heat exchange rela-- tionship with said flatiron.

4, A household electric heatingappliance having aheating element,comprising a metal plate: having awork surface and an oppositesurfacc:and having first and second terminal portions, a vitreous coatingcovering one surface of'said metal plate, a metallic resistancefilmdeposited on said vitreous coating having an' area substan tially thesame as said metal plate, a second metallic film at said first andsecond terminal portions, a housing separate from said appliance, acontrollable space discharge device mounted in said housing and havingan input and an output, means for connecting said input to analternating current source, means for con meeting the output of saidspace discharge device to said metallic film, a control circuit havinginput and output means, means for energizing the input means of saidcontrol circuit from said alternating current source, means forconnecting the output means of said control circuit to said controllablespace discharge device to control the output thereof, said controlcircuit having a temperature responsive impedance in heat exchangerelationship with said appliance.

5. A household electric flatiron, comprising a metal soleplate having awork surface and an opposite surface and having heel and toe portions, a

vitreous coating covering said opposite surface of said soleplate, ametallic resistance film deposited on said vitreous coating having anarea substantially the same as said soleplate, a second vitreous coatingcovering said metallic film, a solid heat-insulating cover substantiallycovering said second vitreous coating, means for providing electricalconnection to said metallic film at said heel and toe portions, firstand second lugs projecting from said opposite surface, a handle fastenedto said first and second lugs, a housing 31 separate from said flatiron,a gaseous grid controlled rectifier mounted in said housing and havingan input and an output, means for connecting said input to analternating current source,

means for connecting the output of said rectifier to said flatiron, aphase shift bridge circuit having input and output means, means forenergiz ing the input means of said bridge circuit from said alternatingcurrent source, means for connect the output means of said bridgecircuit to said controlled rectifier to control the output thereof, saidbridge circuit having four arms, one of said arms having an impedanceresponsive to temperature changes, and means for placing said one arm inheat exchange relationship with said flatiron.

'6. An electronic tube control for a household electric heatingappliance, comprising a housing separate from said appliance, a gaseousgrid controlled rectifier mounted in said housing and having an inputand an output, means for connecting said input to an alternating currentsource, means for filtering the rectified output of said rectifier,means for applying the rectified and filtered rectifier output to aheating element of said appliance, a phase shift bridge circuit havinginput and output means, means for energizing the input means of saidbridge circuit from said alternating current source, means forconnecting the output means of said bridge circuit to said controlledrectifier to control the output thereof, said bridge circuit having atleast one arm, said at least one arm including in electrical circuitrelationship at least a part of said heating element, said at least apart of said heating element having an appreciable, temperaturecoefiicient of impedance, whereby the majority of power applied to saidheating element is derived from said rectifier rather than said bridgecircuit.

7. A control circuit for an electrical apparatus, comprising acontrollable rectifier having an input and an output, means forconnecting said input to an alternating current source, means forapplying the rectifier output to an electrical 12 power consumingcircuit element of said apparatus to pass rectified currenttherethrough, a phase shift bridge circuit having input and outputmeans, means for energizing the input means of said bridge circuit fromsaid alternating current source, means for connecting the output meansof said bridge circuit to said controllable rectifier to control theoutput thereof, said bridge circuit having at least one arm, said atleast one arm including in electrical circuit relationship at least apart of said circuit element, means for preventing the alternatingcurrent component of said rectifier output from influencing theperformance of said bridge circuit, said at least a part of said circuitelement having an appreciable temperature coefiicient of impedance tocontrol said rectifier, whereby the majority of power applied to saidcircuit element is derived from said rectifier rather than said bridgecircuit.

8. A control circuit for a heating element comprising an alternatingcurrent bridge having pairs of input and output terminals, a rectifierdevice having alternating current input means and di rect current outputmeans, means for connecting said alternating current input means of saidrectifier device to an alternating current source, means for connectingsaid direct current output means of said rectifier device to saidheating element to pass rectified current therethrough for heating thesame, at least part of said heating element having an appreciabletemperature coefiicient of impedance, means for electrically connectingat least a part of said temperature responsive impedance to said bridgeas a part thereof such that alternating current is applied to said lastmentioned part, means for connecting the input terminals of said bridgeto said alternating current source, and means for connecting the outputterminals of said bridge to said rectifier device to control the directcurrent output thereof.

9. A control circuit, a bridge having as one branch thereof a directcurrent load circuit, rectifier means controlled by said bridge andsupplying direct current to said direct current load circuit, means forenergizing said rectifier means and all branches of said bridge circuitwith alternating current, said load circuit having an impedanceresponsive to temperature changes and controlling the output of saidrectifier means accordingly.

10. A control circuit, a bridge having as one branch thereof a directcurrent load circuit, rectifier means controlled by said bridge, meansfor energizing said rectifier means and all branches of said bridgecircuit with alternating current,

and means for connecting said direct current load circuit in series withthe output of said rectifier means to receive the rectified outputtherefrom.

GEORGE V. WOODLING.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,276,589 Steinmetz Aug. 20, 1918 1,457,851 Nesbit June 5,1923 1,694,264 Hull Dec. 4, 1928 1,851,692 Zucker Mar. 29, 19321,870,022 Prince Aug. 2, 1932 1,943,088 Power Jan. 9, 1934 1,994,076Kiihle et al. Mar. 12, 1935 2,079,690 Grisdale May 11, 1937 (Otherreferences on following page) Number 13 UNITED STATES PATENTS Name DateJutson et a1 June 8, 1937 Shrader July 13, 1937 Westell Sept. 21, 1937Long June 7, 1938 Knowles Aug. 9, 1938 Waage June 20, 1939 Bagnall Apr.7, 1942 Hutcheson et a1. Apr. 6, 1943 Ashbaugh Sept. 16, 1947 NumberName Date 2,429,453 Crowley Oct. 21, 1947 2,462,207 Mershon Feb. 22,1949 2,467,856 Rich Apr. 19, 1949 5 2,468,080 Klemperer Apr. 26, 19492,475,309 Chalberg July 5, 1949 OTHER REFERENCES Hull, Hot-CathodeThyratrons, General 10 Electric Review, v01. 32, No. 7, July 1929, pages

